Image forming devices including copiers, laser printers, facsimile machines, and the like, include a photoconductive drum (hereinafter referred to as a drum), typically having a rigid cylindrical surface that is coated along a defined length of its outer surface. The surface of the drum is typically charged to a uniform electrical potential and then selectively exposed to light in a pattern corresponding to an original image. Those areas of the photoconductive surface exposed to light are discharged, thus forming a latent electrostatic image on the photoconductive surface.
A developer material, such as toner, having an electrical charge such that the toner is attracted to the photoconductive surface, is brought into contact with the drum's photoconductive surface. A recording sheet, such as a blank sheet of paper or a transfer belt, is then brought into contact with the photoconductive surface and the toner thereon is transferred to the recording sheet in the form of the latent electrostatic image. The recording sheet is then heated thereby permanently fusing the toner.
In preparation for the next image forming cycle, the photoconductive surface is optionally discharged and cleaned of residual toner. A cleaner blade may be positioned adjacent to the drum for mechanically removing any residual toner that has not been transferred during the printing process. Removal of the residual toner is desirable prior to preparing the drum to receive a new image.
In a laser printer, a photoconductive drum is typically used as the source object from which the image is initially formed by dots of laser light impacting the surface of this drum. The photoconductive drum is typically charged to a substantial voltage, such as a voltage greater than 1,000 VDC. This voltage could be either positive or negative with respect to ground, depending upon the charging system and the chemicals used in the photoconductive drum material. Additionally, an AC voltage superimposed on the DC voltage could be used.
For this photoconductive drum to achieve this substantially large voltage, it is typical for a charge roller to be placed into contact with the surface of the photoconductive drum. The charge roller typically comprises a moderately electrically conductive cylinder, or a semiconductive cylinder, which has an electrically conductive center that receives a high voltage from a high voltage power supply. As voltage is received at the electrically conductive center, this voltage charges the entire charge roller, including its outer cylindrical surface. This high voltage at the cylindrical surface of the charge roller is then passed onto the outer surface of the photoconductive drum as the drum rotates.
The ability of the charge roller to charge the photoconductive drum decreases over its life due to roller characteristics and contamination of the surface of the roller. This decrease in voltage may, over time, impact the ability of the photoconductive drum to produce accurate prints. Consequently, it is desirable to reduce buildup of contamination that occurs on the surface of the charge roller which may subsequently decrease charge roller life or reduce print quality.